Adding a linear line of best fit to subplots

I have been looking up matlab help on this but I cant seem to get my head around it. For example when I look at my code I just have:

    plot (SigVal)
So when I try and plot:

polyval(x, y 1)

I have nothing to put between these brackets except "SigVal". Can someone talk me through how I go about adding a line of best fit to this subplot?

thanks

%-------------------------------------- SIG VAL SUBPLOT -------------------    
    figure('name','resultimage');
    Len=1400;
    Wid=600;
    aa=25;
    bb=200;
    set(gcf,'position',[aa bb Len Wid]);

      subplot(2,3,1)
      xmin=1;
      xmax=100;
      plot(SigVal)

      h=plot(SigVal);
      % label max and min values of a 'fn1' on the plot
      xValue = get(h,'XData');
      yValue = get(h,'YData');
      imin = find(min(yValue)==yValue);% find the index for the min and max
      imax = find(max(yValue)==yValue);% values of yValue

      (yValue(imax));
      (yValue(imin));

      % label the max. and min. values  on the plot
      ymax=yValue(imax)+3;
      ymin=yValue(imin)-3;

      y1=ymax-1;
      y2=y1;
      y3=ymin+1;
      maxstr=['max.=',num2str(yValue(imax))];
      minstr=['min.=',num2str(yValue(imin))];

      text(10, y1, maxstr);
      text(50, y2, minstr);

      if Signalstabilitytestfail == 1;
          Test_resultstr = 'Test FAILED';
          text(30, y3, Test_resultstr)
          sigvalteststr='fail';

      else
          Test_resultstr = 'Test passed';
          text(30, y3, Test_resultstr)
          sigvalteststr='pass';

          %warndlg('Signal Stability failed','!! Warning !!')
      end

      axis([xmin xmax ymin ymax]) 
      title('SigVal')

Answer 1

[Image Analyst]

See my attached polyfit demo. I think it should answer your questions.

[Jonathan O'Neill]

Thank you, I found some code you provided to answer another question and followed that...

http://www.mathworks.com/matlabcentral/answers/89335-how-do-i-make-a-best-fit-line-along-with-getting-r-2-on-matlab

I replaced my code and it worked, although it gave me a graph with dots, in order to have the dots connected I did this...

   Changing 

"h=plot(x, y, 'b*', 'LineWidth', 1, 'MarkerSize', 1";

        to 

      "h=SigVal" gave me connected lines and that seems to be all it affected.

%-------------------------------------- SIG VAL SUBPLOT -------------------    
figure('name','resultimage');
Len=1400;
Wid=600;
aa=25;
bb=200;
set(gcf,'position',[aa bb Len Wid]);

subplot(2,3,1)
xmin=1;
xmax=100;

x=1:100
y = SigVal

plot(x, y, 'b*', 'LineWidth', 1, 'MarkerSize', 1);

coeffs = polyfit(x, y, 1);
% Get fitted values
fittedX = linspace(min(x), max(x), 200);
fittedY = polyval(coeffs, fittedX);
% Plot the fitted line
hold on;
plot(fittedX, fittedY, 'r-', 'LineWidth', 1);

********************************************************

%h=plot(x, y, 'b*', 'LineWidth', 1, 'MarkerSize', 1);
h=plot(SigVal);

********************************************************

% label max and min values of a 'fn1' on the plot
xValue = get(h,'XData');
yValue = get(h,'YData');
imin = find(min(yValue)==yValue);% find the index for the min and max
imax = find(max(yValue)==yValue);% values of yValue

(yValue(imax));
(yValue(imin));

% label the max. and min. values  on the plot
ymax=yValue(imax)+1.5;
ymin=yValue(imin)-1.5;

y1=ymax-1;
y2=y1;
y3=ymin+1;
maxstr=['max.=',num2str(yValue(imax))];
minstr=['min.=',num2str(yValue(imin))];

text(10, y1, maxstr);
text(50, y2, minstr);

if Signalstabilitytestfail == 1;
    Test_resultstr = 'Test FAILED';
    text(30, y3, Test_resultstr)
    sigvalteststr='fail';

else
    Test_resultstr = 'Test passed';
    text(30, y3, Test_resultstr)
    sigvalteststr='pass';

end

axis([xmin xmax ymin ymax]) 
title('SigVal')